Viscoelastic damping device

ABSTRACT

The invention relates to a damping device ( 100 ) for damping relative movements between a stay and a structural element of a civil engineering construction, comprising:—a viscoelastic first damping system ( 110 ) for damping a first relative movement component,—a second damping system ( 120 ) in series with the viscoelastic first damping system and for damping a second relative movement or component.

TECHNICAL FIELD

The present invention concerns the field of civil engineering. In particular, the present invention concerns a device and a method for viscous damping enabling the dampening of relative displacements, and in particular oscillations, between a first structural element and a second structural element of a work of construction.

More particularly, but in no way limited thereto, the present invention concerns a device and a method for damping vibrations of cables in a work of construction, such as the stays of a bridge, of a roof, of a suspended walkway, of structural elements potentially subjected to vibrations or large-amplitude displacements or any other suspended work of construction.

STATE OF THE ART

In civil engineering works, different structural elements are frequently subjected to relative displacements, for example relative movements or relative vibrations.

It is known to dampen such relative displacements by using viscoelastic means or means acting by friction.

Thus, for example document FR2 664 920 proposes a damping device for vibrations of a bridge stay. This device acts in a viscoelastic manner and implements a rigid pole mounted at an intermediary point of its length in a fixed sub base so as to be able to oscillate around this point in all directions. The displacements of the pole foot are dampened for example by means of viscoelastic elements. The amplitude of the movements that can be dampened is limited by the sub base at the level of the pole foot. This device does not allow large-amplitude displacements in all directions to be absorbed.

Document EP1035350 describes another type of damping device, forming an internal damper operating by friction, wherein the transverse oscillation movements of a cable are dampened. However, this solution does not make it possible to dampen, within the same damping device, several components of a large-amplitude relative movement between a first structural element and a second structural element of a work of construction.

FR2751673 describes another device comprising an elastic or viscoelastic ring for damping the vibrations of a cable. This device is only adapted for damping small-amplitude vibrations in a plane perpendicular to the cable.

FR2631407 concerns improvements to devices for damping vibrations on stays and implements an annular member mounted on a segment of the stays. A pillow of paste or grease under pressure fills the ring cavity. A rigid structure connects the annular member to a foundation. Again, this device is not suitable for damping large-amplitude displacements along any directions.

It happens that the various structural elements of a work of construction move one relative to the other according to different components, for example by translation along two or three directions or by rotation around two axes, or according to a combination of linearly independent displacements. For example, the stays of a bridge sometimes move along a first direction orthogonal to the stays and directed towards the structural element supported by the stay, for example the bridge span, and along another direction perpendicular to the first direction and to the stay. Displacements of smaller magnitude in the direction of the stay can for example result from dilatations. Some structural elements also experience rotations relative to other structural elements of the same work of construction.

Existing damping devices are however poorly adapted for damping such complex displacements along various components.

BRIEF SUMMARY OF THE INVENTION

One aim of the present invention is to propose a damping device free from the limitations of the known devices and enabling displacements along different components between a first structural element and a second structural element of a work of construction to be dampened.

Another aim of the invention is to enable small and/or large amplitude displacements for each of the components of a complex displacement to be dealt with, with a damping that can be chosen independently for each of these elementary components.

According to the invention, these aims are achieved notably by means of a viscoelastic damping device for damping relative movements between a stay and a structural element of a civil engineering construction work, comprising:

-   -   a first damping system acting mainly for damping a first         relative displacement component between said stay (20) and said         structural element,     -   a second damping system acting mainly for damping a second         relative displacement component between said stay and said         structural element,         wherein the first damping system and the second damping system         are placed in series,         wherein at least one of the damping systems comprises a         viscoelastic damping element.

In this application, two damping systems are considered as placed in series if the first extremity of one system is connected to a fixed point relative to the first extremity of the other system, and if the second extremity of the first system is connected to a point whose displacements relative to the second extremity of the second system one wishes to dampen. In other words, the device comprises an intermediary point connected to the stay by at least a first damping system and connected to the structural element by at least a second damping system; the intermediary point is likely to move in a dampened manner both in relation to the stay and in relation to the structural element.

The invention concerns in particular a device wherein a first extremity of the first system and a first extremity of the second system are connected to one another by a fixed or pivoting connection, wherein a second extremity of the first damping system is connected by a fixed or pivoting connection with a stay and wherein the second extremity of the second system is connected by a fixed or pivoting connection to a structural element, for example a foundation or a bridge deck.

The first structural element can comprise a first element that is fixed or pivoting relative to the stay, a second element capable of moving in translation relative to the first element along a direction perpendicular to the stay and a viscoelastic damping fluid between the first and the second element. The first relative displacement component is thus constituted by a first translation along a first direction (X) extending between the stay and the structural element.

The second element of the first damping system can be constituted by a cylinder. The first element of the first damping system can be constituted by a piston sliding in said cylinder. The viscoelastic damping fluid can be placed in a manner such as it opposes the displacement of said piston in said cylinder. It is possible to invert the position of the cylinder and of the piston, i.e. to connect the cylinder to the stay by a fixed or rotating connection.

The second damping system can comprise a third element and a fourth element capable of moving in rotation relative to the second element around a rotation axis substantially parallel to the stay. One said viscoelastic damping fluid can be provided between the third and the fourth element. The second relative displacement component can then be constituted by a second translation along a third direction, in a plane perpendicular to the stay, and different from the first direction.

The second damping system can be connected by a pivoting articulation to the first damping system.

The first damping system can be connected by a first pivoting articulation to the structural element. The second damping system can comprise one extremity connected by a second pivoting articulation to the structural element, and a second extremity connected by a third pivoting articulation at an intermediary point of the first damping system, so as to exert a force opposing the rotation of the first damping system.

The second damping system can comprise two piston-cylinder assemblies that can for example be placed in parallel or in a triangle. In this embodiment, the first piston-cylinder assembly comprises a cylinder connected by a third articulation pivoting at an intermediary point of the first damping system, and a piston connected by one said second pivoting articulation to said structural element on a first side of the first pivoting articulation. The second piston-cylinder assembly comprises a cylinder connected by a third pivoting articulation to an intermediary point of the first damping system, and a piston connected by one said second pivoting articulation to said structural element on the other side of the first pivoting articulation.

The second relative displacement component can be projected in said device along a rotation, for example a rotation around an axis substantially parallel to the direction of the stay.

A third damping system can be provided for damping a third relative displacement component between said stay and said structural element. In this case, the first damping system, the second damping system and the third damping system are placed in series. The third relative displacement component is different from the first relative displacement component and from the second relative displacement component.

The invention also concerns a civil engineering construction work comprising a stay and a structural element supported by said stay, comprising at least one damping device such as described.

This solution has notably the advantage over the prior art of enabling each component of the relative displacement, and thus each type of corresponding oscillation, to be dealt with independently.

The different movement components to be dampened can be displacement components along different axes, for example translations and/or rotations along different axes.

The first relative displacement component can be constituted by a first translation along a first direction (X) extending between the first structural element and the second structural element.

The second relative displacement component can be constituted by a second translation along a third direction (Y) different from the first direction.

The third direction can be essentially orthogonal to the first direction (X) and to a second direction (Z) tangential to the first structural element.

Additionally, the different movement components to be dampened can be movement components according to different frequencies. For example, a first damping system can be optimized for damping low-frequency displacements whilst another damping system can be optimized for damping higher frequency displacements, for example vibrations.

Advantageously, damping the displacements according to the first component (resp. second component) thanks to the first (resp. second) damping device has no influence on damping the displacements according to the second (resp. first) component by the second (resp. first) damping device in series.

In the case where a third damping system is present, advantageously the damping of the movements along the third (resp. second) component thanks to the third (resp. second) damping system has no influence on damping the displacements according to the second (resp. third) component by the second (resp. third) damping device in series.

Also, in this case, advantageously the damping of the displacements according to the first (resp. third) component thanks to the first (resp. third) damping device has no influence on damping the displacements according to the third (resp. first) component by the third (resp. first) damping device in series.

Each damping system preferably allows a large-amplitude relative displacement along or around a single axis. For example, the first damping system allows a large-amplitude translation along the axis X whilst the second damping system allows a large-amplitude rotation around the axis Z. A translation is considered to be of large amplitude when it exceeds for example 300 mm. A rotation is considered to be of large amplitude when it exceeds for example 5°, preferably 10°. Translations and/or rotations along these main axes are dampened thanks to the viscoelastic fluids.

All the damping systems can comprise a viscoelastic fluid to dampen the displacements between two mobile elements. Alternatively, the device can comprise the connecting in series of at least one viscoelastic damping system with at least one damping system based on the friction between two mobile elements.

At least one of the damping systems can be constituted by two viscoelastic system elements in parallel or in a triangle.

Furthermore, each damping system advantageously comprises guiding elements that enable parts in relative movement to move relative to one another and that preferably furthermore allow small-magnitude displacements along or around at least one axis different from the main axis. For example, the guiding elements of the first damping system can allow small-amplitude translations along the axis Y or small-amplitude rotations around the axis Z. A displacement of less than 10 millimeters or a rotation of less than 1° are for example considered small-amplitude displacements. These additional degrees of freedom limit the constraints on the components of the system depending on the desired damping.

According to a preferred arrangement, the first displacement component is a translation movement along a first direction (X) extending between the first structural element and the second structural element.

According to another preferred arrangement, adopted alone or in combination with the preceding arrangement, the second relative displacement component is a translation movement along a second direction (Y). In the presence of these two preferred arrangements, the second direction (Y) is preferably orthogonal to the first direction (X). Advantageously, this second direction (Y) is essentially orthogonal to the longitudinal direction of the stay.

One of the advantages of the inventive solution is to allow complex relative movements to be dampened, i.e. movements comprising several components, using a single device mounted between a first structural element and a second structural element. It is thus possible to avoid having to use several distinct devices that require a longer assembly and more space which can prove problematic in some configurations of works of construction.

The choice of viscoelastic material used on the one hand within the first damping system and on the other hand within the second damping system makes it possible to determine the amplitude of the damping of the relative movement component in question. In this manner, it is thus possible to determine the operating characteristics of the first (second) damping system, such as the value range for intensity, frequency and/or energy of the relative displacement handled by this first (second) damping system.

In a civil engineering construction work, the stay can be for example a tensioned cable fastened at an anchoring point to the structural element.

Thus, for example, in such a civil engineering construction work, the structural element can be a foundation, or a bridge deck or a structure element integral with a bridge deck, or a suspended roofing element or structure element integral with a suspended roof.

BRIEF DESCRIPTION OF THE FIGURES

Examples of embodiments of the invention are indicated in the description illustrated by the attached figures in which:

FIG. 1 illustrates a first embodiment of the invention representing a damping device in perspective,

FIG. 2 illustrates a second embodiment of the invention in perspective.

DETAILED DESCRIPTION OF EXAMPLES OF EMBODIMENTS

As can be seen in FIG. 1, the damping device 100 according to the first embodiment is mounted in this example between a cable 20 or stay and a structural element 30, for example a foundation, a slab, the deck of a suspended bridge or else a part mounted integrally with such a deck. The cable can be connected to a pylon or strut (not represented).

With respect to the stay 20, the damping device 100 is mounted for example by a sleeve 101 enclosing the stay 20 and forming a first anchoring point A1. The sleeve 101 is connected to the stay. The damping device is thus connected to the stay and can thus be fixed relative to the stay, capable of sliding longitudinally along this stay or also capable of pivoting relative to this stay, for example around the axis Z tangential to the stay or an axis X or Y perpendicular to the stay.

With respect to the structural element 30, the damping device 100 is mounted for example by a mounting flange 102 welded or riveted to the structural element 30 and forming a second anchoring point A2. A pivoting connection to the structural element 30 can also be conceived.

The damping device 100 thus connects the first anchoring point A1 to the second anchoring point A2 along a first direction X corresponding to the longitudinal direction or main direction of the damping device 100. In this arrangement, a second direction (Z) is defined by the stay 20 and is orthogonal to the first direction (X). A third direction (Y) orthogonal to the first direction (X) and to the second direction (Z) is also defined. In practice, the plane (X, Y) containing the first direction (X) and the third direction (Y) corresponds to the plane normal to the tangent of the stay 20 at the point A1. Typically, the stay is subjected to movements of greater amplitude in this plane X-Y than along the second direction (Z).

In this first embodiment illustrated in FIG. 1, the damping device 100 is comprised of a first damping system 110 situated in the part of the damping device 100 adjacent to the stay 20 (upper part of the damping device 100 in FIG. 1) and of a second damping system 120 situated in the part of the damping device 100 adjacent to the structural element 30 (lower part of the damping device 100 in FIG. 1). As will be described in detail hereinafter, the first damping system 110 makes it possible here to absorb and dampen the translation component between the stay 20 and the structural element 30 along the first direction X, for example slow displacements or oscillations along the axis X.

As for the second damping system 120, it makes it possible to absorb and dampen the displacements of the cable along the axis Y, by projecting them in the form of rotation around the axis Z of an intermediate member 103 relative to the remaining assembly 120. This second damping system also allows relatively slow displacements or higher-frequency vibrations to be dampened.

The intermediate member 103 is thus capable of moving both relative to the stay 20 and relative to the structural element 30. This intermediate member constitutes a first extremity of each of the two damping systems 110, 120 which are thus placed in series.

In this example, the intermediate member 103 is common to the first damping system 110 and to the second damping system 120 which it connects.

The intermediate member 103 can constitute for example an element of the type piston capable of sliding along the axis X in an element of the type cylinder of the first damping system 110. A viscoelastic fluid in this cylinder, for example a gel or an oil under pressure, opposes this displacement by thus damping the displacements of the stay along the axis X. The damping force is generated by viscous losses when the fluid is forced to move through a passage of calibration section during the displacement of the piston. The piston's run can be for example of 50 to 1000 mm in order to dampen large-amplitude displacements. The maximum damping force can be comprised for example between 1 kN and 200 kN.

The intermediate member 103 can also constitute a piston of the second damping system 120, capable of pivoting around the axis R substantially parallel to Z in a cylinder or a base within the system 120, for example in the manner indicated in document FR 2 664 920. In the same way as in the first damping system, a viscoelastic fluid in this cylinder opposes the displacements of this piston and thus dampens the rotations of the second damping system around the axis R and thus the translations of the stay along the axis Y.

It is also possible to provide two damping systems 110, 120 in series that use two distinct pistons rather than a common member 103. Furthermore, it is possible to invert the position of the cylinder and of the piston in one of the damping systems or in both damping systems. For example, the first damping system could comprise a piston connected to the stay 20 and a cylinder connected to the intermediary point 103. The second damping system could comprise a piston connected to the structural element 30 and a cylinder connected to the intermediary point 103. The two damping systems 100, 110 can be connected to one another by an articulated connection, for example a pivot.

Guiding elements, not represented, can be provided to allow the intermediate member 103 a relative displacement relative to the stay 20 that is not constituted purely of a translation along the axis X; a translation of limited amplitude along the axis Y, or even a rotation of limited angle around the axis Z, are possible.

In the same way, guiding means of the intermediate member 103 relative to the structural element 30 allow a limited freedom of translation and/or rotation of the intermediate member 103 relative to the structural element 30.

Thanks to these guiding elements at each articulation, the displacement components for the movement of the stay 20 relative to the structural element 30 that do not need to be dampened are left free or are restrained by low stiffness or mildly rigid mechanical connections. Typically, the force, resp. the torque, required for a displacement along an axis other than that which needs to be dampened is on the order of 1 to 15% of the force, resp. of the torque, that is necessary for a displacement of 3 to 500 mm, or of 1° to 15°, along the dampened direction.

With such an arrangement, the damping device 100 according to the invention can accept large-amplitude translation movements along the axis X whereas the known external friction damping devices are usable up to movement values along the axis X on the order of 50 mm (millimeters) above and below the mean position. Thus, the damping device 100 according to the invention makes it possible to dampen a vertical movement of the cable 20 beyond 50 mm, for example up to 500 mm, even up to 700 mm or up to 1000 mm, even beyond that.

With such an arrangement, the damping device 100 can furthermore accept rotation movements of the intermediate member 103 along the axis R with an angle value sufficient for compensating large amplitudes of displacement of the cable along the second direction Y. In one example, the maximum rotation angle is on the order of +−15° relative to the mean position, i.e. an angular displacement of 30°. Depending on the length of the components, this angular displacement makes it possible to compensate for a translation component of the cable along the second direction on the order of −500 mm to +500 mm. Angles of 10° (angular displacement of 20°), of 25° (angular displacement of 50°), or even up to 30° (angular displacement of 60°) can also be considered, as can different maximum amplitudes depending on the direction relative to the resting position.

It will be understood that the displacement movement of the stay 20 can be decomposed in three elementary translation movements respectively along the first direction X, the second direction Z and the third direction Y. The stay's rotation movements are generally much smaller and can generally be neglected. The three translation components, and the possible rotation components, are dampened thanks to the three components of the movement allowed respectively by the first damping system (translation component along the first direction X), the second damping system (rotation component around the axis R to compensate for the elementary movement along the third direction Y). Thus, the X translation component of the cable is dampened essentially by the first damping system whilst the Y translation component (perpendicular to X and to the cable) is essentially dampened by the second damping system. The Z translation component of the cable is generally considerably smaller than the X and Y components.

The damping device described here above thus comprises a first element 113 integrally united with the first structural element 20, a second element 123 integrally united with the second structural element 30 and an intermediate member 103 capable of translating along a linear axis relative to the first element 113 and capable of pivoting around an axis relative to the second element 123. Means for guiding the intermediate member 103 relative to the first element 113 allow a limited freedom of translation along the axis Y and/or Z and/or of rotation of the intermediate member 103 relative to the first element 113.

The intermediate member can also be replaced by different components assembled or articulated to one another.

Additional degrees of freedom can be provided. For example, the first damping system 110 can be free in rotation and/or translation relative to the stay 20. In the same way, the second damping system 120 can be free in rotation and/or translation relative to the structural element 30. Additional damping systems can be mounted serially with the first or second damping systems 110, 120 in order to dampen other displacement components. Damping systems in parallel with any of the first or second damping systems 110, 120 can also be considered in the case of large forces or torques.

Attention is now turned to a second embodiment illustrated schematically in FIG. 2. This damping device 110 replicates some arrangements of the damping device 110 so that the elements that are common to these two embodiments bear identical reference signs.

In this embodiment, the first damping system 110 is constituted by a viscoelastic damper connected through an articulated connection 160 to a sleeve 101 mounted on the stay 20. This first damping system 110 extends along the axis X perpendicular to the tangent of the stay in the direction of the structural element 30. It thus allows displacements and vibrations of the stay 20 along this axis X to be dampened. In the illustrated example, the first damping system comprises a viscoelastic piston-cylinder assembly with a piston 110A connected to the articulation 160 and a cylinder 110B connected in an articulated manner by the connection 300 to the structural element 30. It is also possible to invert this arrangement and to connect the cylinder to the stay by placing the piston on the side of the structural element 30. Furthermore, it is possible to provide a first damping system 110 without articulated connection with the structural element 30.

The second damping system 120 comprises in this example two piston-cylinder assemblies mounted in a triangle. One extremity of each piston-cylinder assembly 120 is connected in an articulated manner via the pivoting articulation 140 to the flange 170 mounted on an intermediary point of the first damping system, for example close to the extremity of the cylinder 110B on the side of the piston 110A. The other extremity of this assembly is connected in an articulated manner via the pivoting articulation 150 to the structural element 30. In this example, one of the piston-cylinder assemblies 120 is mounted on the structural element 30 on one side of the articulation 300 whilst the other piston-cylinder assembly 120 is mounted on the structural element 30 on the other side of the articulation 300; the arrangement thus forms a triangle. In the illustrated example, the two piston-cylinder assemblies 120 are mounted with the piston 120A on the side of the structural element 30 and the cylinder 120B on the side of the flange 170; it is however possible to invert this structure.

The first damping system 110 can thus pivot around the articulation 300 so as to follow the displacements of the stay along the axis Y (the axis Y being perpendicular to the stay and to the longitudinal axis X). The second damping system 120 allows these movements to be dampened. Indeed, the rotations of the first damping system 110 cause a compression of one of the piston-cylinder assemblies 120 and an extension of the other assembly, which are opposed by the viscoelastic fluids in the cylinders 120B.

It is also possible in the frame of the invention to provide a third damping system, for example at the articulated connection between the first damping system 110 and the sleeve 101.

The present invention also concerns a civil engineering construction work with a stay 20 that is mounted on the structural element 30 at the location of an anchoring point, with the damping device 100 being mounted between said stay 20 and said structural element 30 in a manner removed from said aforementioned anchoring point. This type of arrangement corresponds to a damping device called “external damping device” in contrast to other types of damping devices, called “internal damping devices” that are an integral part of the stay or concentric around this stay, as in document EP1035350.

REFERENCE NUMBERS USED IN THE FIGURES

-   20 Stay -   30 Structural element (foundation) -   X First direction -   Z Second direction -   Y Third direction -   101 Sleeve -   110 First damping system -   110A Piston of the first damping system -   110B Cylinder of the first damping system -   120 Second damping system -   120A Piston of the second damping system -   120B Cylinder of the second damping system -   130 Third damping system -   131 Rotation axis in Y (material shaft) -   140 Third pivoting articulation -   150 Second pivoting articulation -   160 Articulated connection on the sleeve -   170 Flange -   300 First pivoting articulation 

1. Viscoelastic damping device for damping relative movements between a stay and a structural element of a civil engineering construction work, said structural element being supported by said stay, comprising: a first damping system acting mainly for damping a first relative displacement component between said stay and said structural element, a second damping system acting mainly for damping a second relative displacement component between said stay and said structural element, wherein the first damping system and the second damping system are placed in series, said device comprising an intermediary point connected both to the stay by at least said first damping system and to the structural element by at least said second damping system, whereby the intermediary point is likely to move in a dampened manner both in relation to the stay and in relation to the structural element, wherein at least one of the damping systems comprises a viscoelastic damping element.
 2. Damping device according to claim 1, wherein the first damping system comprises a first element fixed relative to the stay, a second clement capable of moving in translation relative to the first element along a direction perpendicular to the stay, and a said viscoelastic damping fluid between the first and the second element; wherein said first relative displacement component is constituted by a first translation along a first direction extending between said stay and said structural element.
 3. Damping device according claim 2, wherein said second element is constituted by a cylinder, wherein said first element is constituted by a piston sliding in said cylinder, and wherein said viscoelastic damping fluid is placed so as to oppose the displacement of said piston in said cylinder.
 4. Damping device according to claim 1, wherein the second damping system comprises a third element, a fourth element capable of pivoting relative to the third element around a rotation axis substantially parallel to the stay, and a said viscoelastic damping fluid between the third and the fourth element, wherein said second relative displacement component is constituted by a second translation along a third direction perpendicular to the stay and different from the first direction.
 5. Damping device according to claim 1, wherein the second damping system is connected by a pivoting articulation to the first damping system.
 6. Damping device according to claim 1, wherein the first clamping system is connected by a first pivoting articulation to said structural element, and wherein the second damping system comprises an extremity connected by a second pivoting articulation to said structural element, and a second extremity connected by a third pivoting articulation to an intermediary point of the first damping system, so as to exert a force opposing the rotation of the first damping system.
 7. Damping device according to claim 6, wherein the second damping system comprises two piston-cylinder assemblies, wherein the first piston-cylinder assembly comprises a cylinder connected by a third pivoting articulation to an intermediary point of the first damping system, and a piston connected by a second pivoting articulation to said structural element on a first side of the first pivoting articulation; wherein the second piston-cylinder assembly comprises a cylinder connected by a third pivoting articulation to an intermediary point of the first damping system, and a piston connected by a said second pivoting articulation to said structural element on the other side of the first pivoting articulation.
 8. Damping device according to claim 6, wherein the second damping system comprises two piston-cylinder assemblies, wherein the first piston-cylinder assembly comprises a piston connected by a third pivoting articulation to an intermediary point of the first damping system, and a cylinder connected by a second pivoting articulation to said structural element on a first side of the first pivoting articulation; wherein the second piston-cylinder assembly comprises a piston connected by a third pivoting articulation to an intermediary point of the first damping system, and a cylinder connected by a said second pivoting articulation to said structural element on the other side of the first pivoting articulation.
 9. Damping device according to claim 4, wherein said second relative displacement component is projected in said device along said rotation, wherein said rotation is performed around an axis substantially parallel to the second direction.
 10. Damping device according to claim 1, wherein it further comprises a third damping system for damping a third relative displacement component between said stay and said structural element, wherein the first damping system, the second damping system and the third damping system are placed in series, and wherein the third relative displacement component is different from the first relative displacement component and from the second relative displacement component.
 11. Damping device according to claim 1, wherein the second damping system comprises two piston-cylinder assemblies in a triangle.
 12. Civil engineering construction work comprising a stay and a structural element, wherein it comprises at least one damping device according to claim
 1. 13. Civil engineering construction work according to claim 12, wherein said structural element is a foundation, a bridge deck or a suspended roof. 